Hi Kenton,
Thanks for the advice.
This is what I ended up with:
template <typename T>
class SharedMessageBuilder {
public:
SharedMessageBuilder() :
message_builder(boost::make_shared<capnp::MallocMessageBuilder>())
{};
inline capnp::BuilderFor<T> getRoot() const {
return message_builder->template getRoot<T>();
};
private:
boost::shared_ptr<capnp::MallocMessageBuilder> message_builder;
};
Then in each task, I create an instance and fill it out:
auto mb = SharedMessageBuilder<::Status::Amp>();
auto amp_status = mb.getRoot();
…
then in the caller/collector, I copy the data (where amp_status_f, is a
boost::future<SharedMessageBuilder<::Status::Amp>>):
capnp::MallocMessageBuilder message;
auto status = message.initRoot<Status>();
status.setAmp(amp_status_f.get().getRoot().asReader());
Thanks again,
Adam
On Mon, Feb 13, 2017 at 1:13 PM, Kenton Varda <[email protected]> wrote:
> Hi Adam,
>
> Sorry for the long delay in replying.
>
> You are correct that MessageBuilder is *not* thread-safe. For example,
> memory allocation within a MessageBuilder allocates sequentially out of a
> pre-allocated memory segment, and the allocation counter is not protected
> by any locks.
>
> The POCS idea hasn't been implemented yet, unfortunately.
>
> I think you will need each task to have its own MessageBuilder where it
> constructs its particular sub-message (though it might as well be the root
> of the task's MessageBuilder). Then, when you construct the overall
> message, you'll need to copy the sub-messages into place. E.g.:
>
> mergedBuilder.getRoot<MergedMessage>.setTask1(task1Builder.getRoot<
> Task1Message>());
>
> -Kenton
>
> On Fri, Jan 27, 2017 at 7:53 PM, <[email protected]> wrote:
>
>> Had a few spare hours to have another bash at it.
>>
>> In the seems-to-work-but-I-have-no-idea-what-I'm-doing category…
>>
>> template <typename T>
>> class SharedOrphan {
>> public:
>> SharedOrphan(std::shared_ptr<capnp::MallocMessageBuilder> mb, capnp::
>> Orphan<T>& orphan) :
>> message_builder(mb), orphan(std::move(orphan))
>> {};
>>
>> inline capnp::BuilderFor<T> get() {
>> return orphan.get();
>> };
>>
>> inline capnp::ReaderFor<T> getReader() const {
>> return orphan.getReader();
>> };
>>
>> private:
>> std::shared_ptr<capnp::MallocMessageBuilder> message_builder;
>> capnp::Orphan<T> orphan;
>> };
>>
>> SharedOrphan<::Status::Amp> amp_status() {
>> std::shared_ptr<capnp::MallocMessageBuilder> mb = std::shared_ptr<
>> capnp::MallocMessageBuilder>(new capnp::MallocMessageBuilder());
>> //std::make_shared<capnp::MallocMessageBuilder>();
>>
>> auto amp_status_o = mb->getOrphanage().newOrphan<::Status::Amp>();
>> auto amp_status = amp_status_o.get();
>>
>> auto zones = amp_status.initZones(6);
>>
>> for (auto z: zones) {
>> z.setId("zone ID");
>> z.setVolume(10);
>> }
>>
>> return SharedOrphan<::Status::Amp>(mb, amp_status_o);
>> }
>>
>>
>> SharedOrphan<::Status::HDMI> hdmi_status() {
>> std::shared_ptr<capnp::MallocMessageBuilder> mb = std::shared_ptr<
>> capnp::MallocMessageBuilder>(new capnp::MallocMessageBuilder());
>> //std::make_shared<capnp::MallocMessageBuilder>();
>>
>> auto hdmi_status_o = mb->getOrphanage().newOrphan<::Status::HDMI>();
>>
>> return SharedOrphan<::Status::HDMI>(mb, hdmi_status_o);
>> }
>>
>>
>> void broadcast_status() {
>> capnp::MallocMessageBuilder mb;
>>
>> auto status = mb.initRoot<Status>();
>>
>> auto amp_status_f = boost::async(boost::launch::async, amp_status).
>> share();
>> auto hdmi_status_f = boost::async(boost::launch::async, hdmi_status).
>> share();
>>
>> auto all_f = boost::when_all(amp_status_f, hdmi_status_f);
>> auto str = all_f.then([&](decltype(all_f)) {
>>
>> status.setAmp(amp_status_f.get().getReader());
>> status.setHdmi(hdmi_status_f.get().getReader());
>>
>> return status;
>>
>> }).get().toString();
>>
>> std::cout << str.flatten().cStr() << std::endl;
>> }
>>
>>
>> The resulting message is built correctly. And I'm assuming that since I'm
>> passing around both the Orphan and the backing MessageBuilder, that there
>> are no use-after-free issues with this.
>>
>> - Adam
>>
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>>
>
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